Screw vacuum pump

ABSTRACT

A screw vacuum pump includes a male rotor, a female rotor, a stator, and a drive motor/motors. A screw gear portion of the male rotor, a screw gear portion of the female rotor, and the stator cooperatively form a gas working chamber. The stator has an inlet port and an outlet port. At least one of the male rotor and the female rotor has a rotor hollow portion which is opened on at least one end face side in a rotation-axis longitudinal direction of the male rotor and/or the female rotor. The drive motor is at least partially received in the rotor hollow portion.

TECHNICAL FIELD

This invention relates to a screw vacuum pump.

BACKGROUND ART

In a semiconductor device manufacturing apparatus, a liquid crystalpanel manufacturing apparatus, or a solar panel manufacturing apparatus,a serious problem arises in a device manufacturing process if oilbackflow occurs from a pump into a process chamber of the devicemanufacturing apparatus. Accordingly, use is generally made of, what iscalled, a dry pump, a mechanical booster pump, or a turbomolecular pumpin which there is no occurrence of contact between suction gas and oil.

However, since molecular weights of process gas, carrier gas, generatedgas, and so on are broad, i.e. from 1 to one hundred and several tens,the current situation is that the above-mentioned pumps are selectivelyused depending on their pumping characteristics for those various gasesand their inherent pumping regions.

On the other hand, since the pumping speed is lowered depending on thekind of gas to be exhausted, a pump having a high pumping speed isinefficiently used and therefore a problem exists that it is notpossible to reduce the power consumption or to place the pump near theapparatus due to the pump size being large.

Further, with respect to general dry pumps and mechanical booster pumps,a serious problem exists that product is deposited inside the pumpbetween an inlet port and an outlet port, resulting in a shortmaintenance time.

In this regard, a screw vacuum pump has a feature that it can be used ina region from the atmospheric pressure to 0.5 Pa and that it is possibleto prevent the pressure in the pump from sharply increasing near anoutlet port, to prevent abnormal heat generation, and to reduce thepower consumption, and has a feature that even if a large amount ofproduct is formed, it is possible to rake out the product to theexterior of the pump by screw tooth surfaces.

Conventionally, as such a screw vacuum pump, there is known a screwvacuum pump described in Patent Document 1.

This conventional screw vacuum pump comprises a male rotor and a femalerotor engaging each other, a stator receiving therein the male rotor andthe female rotor, a first shaft and a second shaft serving as rotationshafts of the male rotor and the female rotor, bearings for the firstshaft and the second shaft, and a drive motor for rotating the firstshaft and the second shaft.

The bearings and the drive motor are disposed outside the male rotor orthe female rotor, i.e. the male rotor or the female rotor, the bearings,and the drive motor are aligned in a rotation-axis longitudinaldirection.

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PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-2004-263629

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, since the male rotor or the female rotor, the bearings, and thedrive motor are aligned in the rotation-axis longitudinal direction inthe conventional screw vacuum pump, there has been a problem that thepump size in the rotation-axis longitudinal direction becomes large.

While the pump is running, drive heat is generated from the drive motor.Consequently, members or devices around the drive motor should bedesigned taking into account the influence of this drive heat of thedrive motor. As a result, there has been a problem that the flexibilityof design of the pump components is impaired.

Therefore, this invention is intended to solve the conventionalproblems, that is, it is an object of this invention to achieve areduction in pump size in the rotation-axis longitudinal direction.

It is another object of this invention to provide a screw vacuum pumpthat ensures the flexibility of design of pump components.

Means for Solving the Problem

A screw vacuum pump of the present invention comprises a male rotor anda female rotor respectively having, on their outer peripheral sides,screw gear portions engaging each other, a stator receiving therein themale rotor and the female rotor, and a drive motor/motors for rotatingthe male rotor and the female rotor, wherein the screw gear portion ofthe male rotor, the screw gear portion of the female rotor, and thestator cooperatively form a gas working chamber, the stator has an inletport and an outlet port adapted to communicate with one end and theother end of the gas working chamber, at least one of the male rotor andthe female rotor has a rotor hollow portion which is opened on at leastone end face side of the male rotor and/or the female rotor in arotation-axis longitudinal direction, and the drive motor is at leastpartially received in the rotor hollow portion, and thus, resolved theforegoing problems. If a structure is employed in which the hollowportions are provided in both male and female rotors and the motors areplaced in the respective hollow portions (i.e. the number of motors istwo), heat rise due to heat generation of the motors becomes uniform inthe male rotor and the female rotor, resulting in the same thermalexpansion, thus achieving an effect that an engagement gap therebetweenis maintained uniform. On the other hand, if a structure is employed inwhich the hollow portion is provided in one of the male rotor and thefemale rotor and the motor is placed in the hollow portion (i.e. thenumber of motors is one), it is possible to suppress the motor costwhile reducing the pump size and increasing the flexibility ofinstallation of an exhaust system.

Effect of the Invention

According to this invention, since the drive motor/motors is/are atleast partially received in the rotor hollow portion/portions, it ispossible to reduce the pump size in the rotation-axis longitudinaldirection. Further, since it is possible to make most of the drive heatof the drive motor/motors stay inside the male rotor or/and the femalerotor and thus to reduce the influence of the drive heat of the drivemotor/motors on the pump components other than the male rotor and thefemale rotor, it is possible to achieve high flexibility of design ofthe pump components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically showing a screw vacuum pumpaccording to a first embodiment of this invention.

FIG. 2 is an explanatory diagram conceptually showing circulation pathsof lubricating oil.

FIG. 3 is a perspective view showing a male rotor.

FIG. 4 is an explanatory diagram exemplarily showing screw gear portionsof the male rotor and a female rotor.

FIG. 5 is a perpendicular-to-axis cross-sectional view of the male rotorand the female rotor.

FIG. 6 is a plan view schematically showing a screw vacuum pumpaccording to a second embodiment of this invention.

FIG. 7 is a perspective view showing a male rotor of a screw vacuum pumpaccording to a modification of this invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, embodiments of this invention will be described withreference to the drawings.

First Embodiment

First, as shown in FIGS. 1 and 2, a screw vacuum pump 100 according to afirst embodiment of this invention comprises a pair of a male rotor 110and a female rotor 120 that are disposed in engagement with each otherwhile maintaining an engagement gap therebetween and are rotatedsynchronously in opposite directions (driven synchronously by anon-illustrated inverter), a stator 130 receiving therein the male rotor110 and the female rotor 120, drive motors 140A and 140B for rotatingthe male rotor 110 and the female rotor 120, rotation shafts (rotationaxes) 150A and 150B fixed to the male rotor 110 and the female rotor120, bearings 160Aa, 160Ab, 160Ac, 160Ba, 160Bb, and 160Bc for therotation shafts 150A and 150B, a pair of gears 170A and 170B (whichprevent contact between the male and female screw rotors in abnormalityand, in particular, which significantly reduce vibration and noise dueto backlash of gears at the time of starting and stopping rotation ofthe rotors) attached to one-end portions of the rotation shafts 150A and150B, oil supply means 180 for supplying lubricating oil tolater-described pump components by centrifugal force due to rotation ofthe rotation shafts 150A and 150B, and a cooling device 190 forwater-cooling the lubricating oil.

The male rotor 110, the female rotor 120, and the stator 130cooperatively form a gas working chamber which transfers and compressesa gas.

As shown in FIGS. 1, 3, and 4, the male rotor 110 and the female rotor120 respectively have, on their outer peripheral sides, screw gearportions 111 and 121 which engage each other while maintaining anengagement gap therebetween.

As shown in FIGS. 1, 3, and 4, the screw gear portions 111 and 121 ofthe male rotor 110 and the female rotor 120 each comprise an unequallead unequal inclination angle screw portion 111 a, 121 a disposed on aninlet port 134 side for transferring and compressing a gas, and an equallead screw portion 111 b, 121 b with one lead or a plurality of leadswhich is continuous with the unequal lead unequal inclination anglescrew portion 111 a, 121 a for transferring the gas.

In the unequal lead unequal inclination angle screw portions 111 a and121 a, a tooth lead angle changes according to a rotation angle of themale rotor 110 and the female rotor 120 so that the volume of a V-shapedgas working chamber formed by the male rotor 110, the female rotor 120,and the stator 130 changes to decrease, thereby carrying out transferand compression and carrying out compression and exhaust near an outletport 135.

In the unequal lead unequal inclination angle screw portions 111 a and121 a, since transfer, compression, and exhaust are carried out, thetemperature of the male rotor 110 and the female rotor 120 becomesuniform.

As shown in FIGS. 1, 3, and 4, the male rotor 110 and the female rotor120 have rotor hollow portions 112 and 122 which are opened on both endface sides of at least one of the male rotor 110 and the female rotor120 in a rotation-axis longitudinal direction, i.e. which pass throughthe male rotor 110 and the female rotor 120 in the rotation-axislongitudinal direction.

The perpendicular-to-axis cross-sectional shape of each of the rotorhollow portions 112 and 122 is circular.

As shown in FIG. 1, the stator 130 comprises a stator body portion 131receiving therein the male rotor 110 and the female rotor 120, a firstsupport portion 132 fixed to the stator 130 and supporting the drivemotors 140A and 140B and the bearings 160Aa, 160Ab, 160Ba, and 160Bb, asecond support portion 133 fixed to the stator 130 and supporting thebearings 160Ac and 160Bc, and the inlet port 134 and the outlet port 135formed in the stator body portion 131 for communicating with one end andthe other end of a gas working chamber.

As shown in FIG. 1, the first support portion 132 is partially receivedin the rotor hollow portions 112 and 122.

As shown in FIG. 1, the drive motors 140A and 140B are partiallyreceived in the rotor hollow portions 112 and 122 of the male rotor 110and the female rotor 120, respectively, and are synchronously controlledby the inverter (not illustrated).

As shown in FIG. 1, the drive motor 140A is disposed between thebearings 160Aa and 160Ab.

As shown in FIG. 1, the drive motor 140B is disposed between thebearings 160Ba and 160Bb.

As shown in FIG. 1, the rotation shafts 150A and 150B are partiallyreceived in the rotor hollow portions 112 and 122.

As shown in FIG. 1, the rotation shafts 150A and 150B respectively haveflange portions 151A and 151B extending toward and fixed to innerperipheral walls of the rotor hollow portions 112 and 122.

As shown in FIG. 1, the bearing mechanisms of the rotation shafts 150Aand 150B are formed by the bearings 160Aa and 160Ba disposed on theinlet port 134 side, the bearings 160Ac and 160Bc disposed on the outletport 135 side, and the bearings 160Ab and 160Bb disposed between thebearings 160Aa and 160Ac and between the bearings 160Ba and 160Bc.

The gears 170A and 170B are attached to the rotation shafts 150A and150B and function to prevent contact between the screw gear portion 111of the male rotor 110 and the screw gear portion 121 of the female rotor120 at the time of occurrence of abnormality and in particular to reducevibration and noise due to backlash of the screw gear portions 111 and121 at the time of starting and stopping rotation of the male and femalerotors 110 and 120.

The oil supply means 180 serves to supply the lubricating oil to thepump components and, as shown in FIG. 2, comprises an oil storageportion 181 storing the lubricating oil, push-up heads 182 each forpushing up the lubricating oil from the oil storage portion 181 bycentrifugal force and drag effect, and oil flow paths 183 each forsupplying the lubricating oil, pushed up by the push-up head 182, to thepump components.

FIG. 2 is a diagram for conceptually explaining the circulation paths ofthe lubricating oil by hatching the respective portions associated withthe circulation paths of the lubricating oil. In FIG. 2, arrows aregiven for conceptually explaining the circulation paths of thelubricating oil, but not for showing specific circulation paths of thelubricating oil.

As shown in FIG. 2, the oil storage portion 181 is a space formed in thelower part of the stator 130 for storing the lubricating oil. In thisoil storage portion 181, a cooling pipe 191 of the later-describedcooling device 190 is disposed.

As shown in FIG. 2, each push-up head 182 has a through hole passingthrough in a vertical direction and an inner peripheral surface of thisthrough hole is formed in a tapered shape which increases in diameterfrom lower to upper. The push-up heads 182 are fixed to lower ends ofthe rotation shafts 150A and 150B so that while the screw vacuum pump100 is driven, the push-up heads 182 are configured to rotate along withthe rotation shafts 150A and 150B, thereby pushing up the lubricatingoil from the oil storage portion 181 by the tapered inner peripheralsurfaces, centrifugal force due to the rotation of the rotation shafts150A and 150B, and the drag effect.

Each oil flow path 183 is a circulation path that is formed at aposition physically isolated from the above-mentioned gas workingchamber, that supplies the lubricating oil, pushed up by the push-uphead 182, to the pump components, and that again returns the lubricatingoil, supplied to the pump components, to the oil storage portion 181.The lubricating oil flows along inner walls defining the oil flow paths183 and simultaneously flows in the form of mist in the hollow oil flowpaths 183. Specifically, in this embodiment, as shown in FIG. 2, thelubricating oil is pushed up from the oil storage portion 181 by thepush-up heads 182 to move upward by centrifugal force in the hollowportions formed in the rotation shafts 150A and 150B and is ejected tothe outside of the rotation shafts 150A and 150B near upper portions ofthe bearings 160Aa and 160Ba. Then, the ejected lubricating oil issupplied into the bearings 160Aa and 160Ba, then flows in the form ofmist in hollow portions formed between the bearings 160Aa and 160Ba andthe drive motors 140A and 140B and simultaneously flows along innerwalls defining the hollow portions, and then is supplied into the drivemotors 140A and 140B. Then, the lubricating oil exiting the drive motors140A and 140B flows in the form of mist in hollow portions formedbetween the drive motors 140A and 140B and the bearings 160Ab and 160Bband simultaneously flows along inner walls defining the hollow portions,and then is supplied into the bearings 160Ab and 160Bb. Then, thelubricating oil exiting the bearings 160Ab and 160Bb flows in the formof mist in hollow portions formed between the bearings 160Ab and 160Bband the synchronous gears 170A and 170B and simultaneously flows alonginner walls defining the hollow portions, and then is supplied to thesynchronous gear 170A, 170B side. The lubricating oil supplied to thesynchronous gear 170A, 170B side is supplied to surfaces of thesynchronous gears 170A and 170B, including a meshing portion between thesynchronous gears 170A and 170B. Then, the lubricating oil is suppliedinto the bearings 160Ac and 160Bc and is again returned to the oilstorage portion 181. Lubricating oil supply portions may be arbitrarilyset according to a carrying-out mode.

The cooling device 190 is for water-cooling the lubricating oil storedin the oil storage portion 181 and, as shown in FIG. 2, comprises thecooling pipe 191 disposed in the oil storage portion 181 for circulatingcooling water and a cooling pump 192 for supplying the cooling waterinto the cooling pipe 191. In FIG. 1, illustration of the cooling device190 is omitted.

As shown in FIG. 5, engagement of the male rotor 110 and the femalerotor 120 is located outside gear engagement pitch circles SA and SBdetermined by a distance between the rotation shaft (rotation axis) 150Aof the male rotor 110 and the rotation shaft (rotation axis) 150B of thefemale rotor 120 and the numbers of teeth of the male rotor 110 and thefemale rotor 120.

As a consequence, there are no tooth surfaces where the tooth-surfacespeeds of the screw gear portion 111 and the screw gear portion 121 areequal to each other, thereby achieving an operation of raking out suckedreaction product or the like and thus achieving an effect of raking outthe reaction product to the exterior of the pump.

Symbols DA and DB shown in FIG. 5 represent the outer diameters of themale rotor 110 and the female rotor 120.

In this embodiment thus obtained, since the drive motors 140A and 140Bare partially received in the rotor hollow portions 112 and 122, it ispossible to reduce the pump size in the rotation-axis longitudinaldirection.

Since it is possible to make most of the drive heat of the drive motors140A and 140B stay inside the male rotor 110 and the female rotor 120and thus to reduce the influence of the drive heat of the drive motors140A and 140B on the pump components other than the male rotor 110 andthe female rotor 120, it is possible to achieve high flexibility ofdesign of the pump components.

Further, since the drive motors 140A and 140B are partially received inthe rotor hollow portions 112 and 122, the drive heat generated from thedrive motors 140A and 140B causes the temperature of the screw gearportions 111 and 121 of the male rotor 110 and the female rotor 120 tobe uniform so that thermal expansion of the screw gear portion 111 ofthe male rotor 110 and that of the screw gear portion 121 of the femalerotor 120 can be maintained on the same level. Therefore, the engagementgap between the screw gear portions 111 and 121 of the male rotor 110and the female rotor 120 is maintained uniform without localization. Asa consequence, there is no engagement contact between the screw gearportions 111 and 121 so that the engagement gap is made stable and,therefore, it is possible to prevent back diffusion from the outlet port135 side, thereby reducing the power consumption and achieving stableoperation of the screw vacuum pump 100.

The drive motors 140A and 140B are disposed between the bearings 160Aaand 160Ab and between the bearings 160Ba and 160Bb.

This makes it possible to ensure a certain distance between the bearings160Aa and 160Ab and between the bearings 160Ba and 160Bb for reliablyreceiving the rotation shafts and to effectively use spaces between thebearings 160Aa and 160Ab and between the bearings 160Ba and 160Bb asinstallation spaces for the drive motors 140A and 140B, thereby furtherreducing the pump size in the rotation-axis longitudinal direction. Thatis, since the motors are placed inside the screw rotors, the externalsize of the pump can be largely reduced. While a conventional pumpcannot be disposed near a semiconductor device manufacturing apparatus,a liquid crystal panel manufacturing apparatus, or a solar panelmanufacturing apparatus, this motor built-in screw pump can be disposednear the apparatus or under a chamber so that it is possible to largelyimprove an apparatus installation space.

Further, since the male rotor 110 and the female rotor 120 have theunequal lead unequal inclination angle screw portions 111 a and 121 a onthe inlet port 134 side and the equal lead screw portions 111 b and 121b on the outlet port 135 side and since the engagement of the male rotor110 and the female rotor 120 is located outside the gear engagementpitch circles SA and SB determined by the distance between the axes ofthe male rotor 110 and the female rotor 120 and the numbers of teeth ofthe male rotor 110 and the female rotor 120, it is possible to increasethe compression ratio, to obtain the effect of raking out the product,and to maintain the stable pumping speed down to 0.5 Pa.

Second Embodiment

Next, a screw vacuum pump 200 according to a second embodiment of thisinvention will be described with reference to FIG. 6.

Herein, the structures, other than a drive motor 240, of the screwvacuum pump 200 according to the second embodiment are totally the sameas those described above. Therefore, by reading 100 s symbols shown inthe description relating to the screw vacuum pump 100 of the firstembodiment and shown in FIGS. 1 to 5 as 200 s symbols, explanation ofthe structures other than the drive motor 240 is omitted.

As shown in FIG. 6, in the screw vacuum pump 200 according to the secondembodiment of this invention, the single drive motor 240 as a drivesource common to a male rotor 210 and a female rotor 220 is received ina rotor hollow portion 212 formed in the male rotor 210.

The drive motor 240 rotates a rotation shaft 250A and a drive force ofthe drive motor 240 is synchronously transmitted also to a rotationshaft 250B through synchronous gears 270A and 270B. In order to rotatethe other screw rotor, the synchronous gears 270A and 270B are formedlarger in width and stronger than the gears 170A and 1708 of the firstembodiment.

Also in the second embodiment, oil supply means 280 and a cooling device(not illustrated) configured in the same manner as in the firstembodiment are provided. However, since there is no difference otherthan the number of drive motors to be supplied with lubricating oil,illustration and explanation thereof are omitted.

Also in this embodiment, since the motor is placed inside the screwrotor, the external size of the pump can be largely reduced. While aconventional pump cannot be disposed near a semiconductor devicemanufacturing apparatus, a liquid crystal panel manufacturing apparatus,or a solar panel manufacturing apparatus, this motor built-in screw pumpcan be disposed near the apparatus or under a chamber so that it ispossible to largely improve an apparatus installation space.

MODIFICATION

Next, a modification common to the first and second embodiments of thisinvention will be described with reference to FIG. 7.

In the above-mentioned first and second embodiments, as shown in FIGS. 1and 6, the description has been given assuming that the screw gearportions 111 and 121, 211 and 221 of the male rotor 110, 210 and thefemale rotor 120, 220 each have the unequal lead unequal inclinationangle screw portion 111 a, 121 a, 211 a, 221 a and the equal lead screwportion 111 b, 121 b, 211 b, 221 b with one lead or a plurality ofleads.

In this modification, as shown in FIG. 7, screw gear portions 311 and321 of a male rotor 310 and a female rotor 320 each comprise a firstequal lead screw portion 311 a, 321 a which is disposed on an inlet port335 side, an unequal lead unequal inclination angle screw portion 311 b,321 b which is continuous with the first equal lead screw portion 311 a,321 a, and a second equal lead screw portion 311 c, 321 c with one leador a plurality of leads which is continuous with the unequal leadunequal inclination angle screw portion 311 b, 321 b.

FIG. 7 shows only the male rotor 310.

In the first embodiment, the second embodiment, and the modification,the description has been given assuming that the screw gear portions ofthe male rotor and the female rotor each have the unequal lead unequalinclination angle screw portion and the equal lead screw portion.However, each screw gear portion may be designed to have only an unequallead unequal inclination angle screw portion.

Further, size design and combination of an unequal lead unequalinclination angle screw portion and an equal lead screw portion may beproperly set according to a carrying-out mode.

DESCRIPTION OF SYMBOLS

110, 210 male rotor

111, 211 screw gear portion

111 a unequal lead unequal inclination angle screw portion

111 b equal lead screw portion

112, 212 rotor hollow portion

120, 220 female rotor

121, 221 screw gear portion

121 a unequal lead unequal inclination angle screw portion

121 b equal lead screw portion

122, 222 rotor hollow portion

130, 230 stator

131, 231 stator body portion

132, 232 first support portion

133, 233 second support portion

134, 234 inlet port

135, 235 outlet port

140A drive motor

140B drive motor

240 drive motor

150A, 250A rotation shaft

150B, 250B rotation shaft

151A, 251A flange portion

151B, 251B flange portion

160Aa, 260Aa bearing

160Ab, 260Ab bearing

160Ac, 260Ac bearing

160Ba, 260Ba bearing

160Bb, 260Bb bearing

160Bc, 260Bc bearing

170A, 170B gear

270A, 270B synchronous gear

180, 280 oil supply means

181 oil storage portion

182 push-up head

183 oil flow path

190 cooling device

191 cooling pipe

192 cooling pump

310 male rotor

311 screw gear portion

311 a first equal lead screw portion

311 b unequal lead unequal inclination angle screw portion

311 c second equal lead screw portion

312 rotor hollow portion

1. A screw vacuum pump comprising a male rotor and a female rotorrespectively having, on their outer peripheral sides, screw gearportions engaging each other, a stator receiving therein the male rotorand the female rotor, and a drive motor/motors for rotating the malerotor and the female rotor, the screw gear portion of the male rotor,the screw gear portion of the female rotor, and the stator cooperativelyform a gas working chamber, the stator has an inlet port and an outletport adapted to communicate with one end and the other end of the gasworking chamber, at least one of the male rotor and the female rotor hasa rotor hollow portion which is opened on at least one end face side ofthe male rotor and/or the female rotor in a rotation-axis longitudinaldirection, and the drive motor is at least partially received in therotor hollow portion.
 2. The screw vacuum pump according to claim 1,wherein the male rotor and the female rotor respectively have the rotorhollow portions, the drive motors are provided in the number of two, andthe respective drive motors are at least partially received in the rotorhollow portions of the male rotor and the female rotor, respectively. 3.The screw vacuum pump according to claim 1, wherein the screw vacuumpump further comprises rotation shafts at least partially received inthe rotor hollow portion/portions and fixed to at least one of the malerotor and the female rotor and at least two bearings for each of therotation shafts, and wherein the drive motor is disposed between thebearings.
 4. The screw vacuum pump according to claim 1, wherein thestator comprises a stator body portion receiving therein the male rotorand the female rotor and a support portion partially received in therotor hollow portion/portions and supporting the drive motor/motorsand/or the bearings.
 5. The screw vacuum pump according to claim 1,wherein each of the screw gear portions of the male rotor and the femalerotor comprises an unequal lead unequal inclination angle screw portiondisposed on the inlet port side and an equal lead screw portion with onelead or a plurality of leads which is continuous with the unequal leadunequal inclination angle screw portion.
 6. The screw vacuum pumpaccording to claim 1, wherein each of the screw gear portions of themale rotor and the female rotor comprises a first equal lead screwportion disposed on the inlet port side, an unequal lead unequalinclination angle screw portion continuous with the first equal leadscrew portion, and a second equal lead screw portion with one lead or aplurality of leads which is continuous with the unequal lead unequalinclination angle screw portion.
 7. The screw vacuum pump according toclaim 1, wherein engagement of the male rotor and the female rotor islocated outside gear engagement pitch circles determined by a distancebetween a rotation axis of the male rotor and a rotation axis of thefemale rotor and the numbers of teeth of the male rotor and the femalerotor.
 8. The screw vacuum pump according to claim 1, wherein the screwvacuum pump further comprises rotation shafts fixed to at least one ofthe male rotor and the female rotor and oil supply unit for supplyinglubricating oil, and wherein the oil supply means unit comprises an oilstorage portion storing the lubricating oil, push-up heads fixed to therotation shafts for pushing up the lubricating oil from the oil storageportion by the use of rotation of the rotation shafts, and oil flowpaths for supplying the lubricating oil, pushed up by the push-up heads,to predetermined portions.
 9. The screw vacuum pump according to claim8, wherein the screw vacuum pump further comprises a cooling device forcooling the lubricating oil.